Dual purpose transmission line

ABSTRACT

A high-voltage power transmission line in the form of a hollow tubular conductor which serves as a conduit for a high-intensity light beam modulated with data having security requirements. The high voltage of the power line effectively precludes unauthorized access to the data carried by the light beam enclosed therewithin.

AU 233 EX FIPBl 'Jb 45] Oct. 24, 1972 United States Patent HerleiksonPrimary Examiner-Carl D. Quarforth Assistant Examiner-E. E. Lehmann [541DUAL PURPOSE TRANSMISSION LINE [72] Inventor:

Attorney-Edgar J. Brower, Q. Baxter Warner and Howard J. Murray, Jr.

mm N a p 93010 22 Filed: Feb. 6, 1969 21 Appl.No.: 798,858

[57] ABSTRACT A high-voltage power transmission line in the form of a r.m 7 9 2m m 7 um H w 5 10 u" 0 a" 5 n QLM C s m UIIF 1]] 2 8 555 [56]References Cited UNITED STATES PATENTS 3,657,543 4/1972Rose..........................250/199 10 Claims, 2 Drawing FiguresUTILIZATION TO DATA RE PRODUCING DEVICE LIGLIT ELECTRICALLY- CONDUCTIVESUPPORTING LIGHT SOURCE 36 AMPLIFIER 5 MODULATOR DET ECTO R 32 4b JusmHIGH- INTENSITY FIBER -OPTIC$ LIGHT- AMPLIFYI NG BUNDLE ELECTRICALLY-CONDUCTIVE SUPPORTING FROM POWER GENERATING SOURCE Ed mm RING 28DETECTOR a DEMODULATOR 22 AT RECEIVING STATION DUAL PURPOSE TRANSMISSIONLINE STATEMENT OF GOVERNMENT INTEREST The invention described herein maybe manufactured and used by or for the Government of the United Statesof America for governmental purposes without the payment of anyroyalties thereon or therefore.

BACKGROUND OF THE INVENTION It is becoming increasingly difficult totransfer confidential information from one place to another withassurance that it can not be (or has not been) compromised. Papers maybe intercepted and copied, telegraph and telephone wires may be tapped,and radio and television broadcasts may be monitored. Coding of the datais only temporarily successful, since all codes can eventually bebroken. Consequently, some method whereby secrecy of the material beingconveyed can be assured will find widespread utilization.

A large part of the civilized world is covered by a network oftransmission lines connecting power-generat ing plants to the ultimateconsumer. These lines are usually high-voltage cables strung on towersand suspended by insulators. When energized, it is extremely hazardousfor an individual to approach within several feet of such a line, and ofcourse direct contact usually causes a fatal shock. Such conductorswould consequently serve admirably for the transmission of confidentialdata, but unfortunately such a supplemental use has not been practicabledue to the magnitude of the voltages present on the line as well as tothe technical difficulty of working with the high power levelsencountered.

A recent development in the communications field has been the discoverythat light may be transmitted through solid materials for considerabledistances and in other than straight lines. Such a transmitting materialmay be in the form of a flexible rod, and in many cases a number of suchrods are assembled in a bundle, with the intensity of the light carriedthrough each individual being independent of the amount of light beingtransmitted by each remaining rod. This light-transmission technique hasbeen termed fiber-optics," and in practice has been found to involve afairly low loss factor. However, it is obvious that any modulation ofthe transmitted light by an intelligence signal is readily detectable byan individual having access to the transmission medium at any pointtherealong.

SUMMARY OF THE INVENTION The present concept combines thedata-transmission advantages realized from the modulation of ahigh-density light beam with the security against unauthorized dataappropriation afforded by the presence of a high voltage powertransmission line. In a preferred embodiment, the latter is in the formof a hollow tubular conductor, and the light beam passes therethroughbetween the points of data transmission and reception. No access to thedata modulation in the light beam can be obtained without breaking intothe tubular conductor, and such action would in all likelihood result incertain injury or death to any individual making the attempt. Sincepresently installed power transmission lines customarily utilize hollowor tubular conductors, the expense of a change-over is minimal in viewof the extra benefits derived therefrom.

STATEMENT OF THE OBJECTS OF THE INVENTION One object of the presentinvention, therefore, is to provide a dual-purpose line for transmittingboth electrical power and intelligence signals.

Another object of the invention is to provide a highpower transmissionline over which messages may be sent without danger of unauthorizedappropriation.

A further object of the invention is to provide a power transmissionline in the form of a hollow tubular conductor capable of passing ahigh-intensity light beam therethrough, such light beam being modulatedby an intelligence signal.

Other objects, advantages, and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of aportion of an air-filled power transmission line designed to enclose ahigh-intensity light beam therewithin; and

FIG. 2 is a sectional view of a power line enclosing a fiber-opticsbundle, and incorporating one suitable means for boosting or amplifyingthe transmitted light beam to a higher level of intensity.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 of the drawings isillustrated a preferred embodiment of the present concept in the form ofa section of a high-power transmission line designed to operate at alevel of approximately 300,000 volts or above. This line sectioncomprises a hollow tubular conductor 10 having a highly reflective innersurface 12. The latter is desirable in order that the conductor 10 passtherethrough a light beam 14 with a minimum of attenuation. Although theconductor 10 is illustrated in FIG. 1 of the drawings as being filledwith air, it is within the scope of the present concept to utilize othergases (either pressurized or not, as may be desired) or to substitutetherefor some solid light-conducting substance, such as the fiber-opticsbundle 16 shown in FIG. 2.

The conductor 10 is designed to transmit in customary fashion powersupplied thereto over a connection 18 from a generating source (notshown) to a utilization device 20. In accordance with the invention,this same conductor 10 is also employed to transmit the output of adata-modulated light source 21 to a detector and demodulator 22 at somereceiving station, where the demodulated data is supplied to a suitablereproducing device (not shown). I 4

Either the air-filled conductor of FIG. 1 or the fiberoptics bundle ofFIG. 2 may be utilized as the liglittransmission medium, depending tosome extent on the nature and intensity of the particular light source21 employed. Alternatively, a partial vacuum may be established withinthe hollow conductor 10 if the efficiency of transmission is found to beincreased by such an expedient. In any event, one or more booster" unitsmay be needed if the data-modulated light is to be conveyed over anyappreciable distance. One design for such a light-amplifying unit isillustrated in FIG. 2 and identified by the reference numeral 24.

designated as A and B in FIG. 2 of the drawings due to current flow inthe line.

A pair of electrically conductive rings 28 and 30 sup port therebetweenan instrument package composed of a light detector 32, an amplifier andmodulator 34, and a high-intensity light source 36, the ring 28 beinglocated approximately at point A and the ring 30 being locatedapproximately at point B. Operating power for each of the units 32, 34and 36 is derived from the voltage drop between the rings 28 and 30, andsupplied to the units over a pair of conductors 38 and 40, as shown.

The light detector 32 receives light arriving thereat from the source 21through the fiberoptics bundle 16. it demodulates such light, whichdemodulated energy is amplified by the unit 34 and employed to modulatethe high-intensity light source 36. The output of the latter is fed intothe following section of the fiber-optics bundle 16 at a higherintensity than that possessed by the light arriving at the detector 32.

Obviously any necessary number of amplifying units 24 may be employed,depending at least in part on the distance over which the data is to beconveyed to the detector 22 at the receiving station. The high voltagesand currents in the power line are affected only to a slight degree bythe energy loss caused by the unit 24.

Although any suitable high-intensity light sourcemay be employed for theunit 21 '(as well as for the booster source 36) it has been found thatlight produced by a laser possesses unusually desirable qualities inthat it is both coherent and monochromatic, suffering very littleattenuation even when transmitted over considerable distances. It willthus be preferred in many cases for carrying out the objectives of thepresent concept.

Although the power line conductor should be oriented as linearly aspracticable to minimize internal reflections and consequent lightattenuation, it is possible at or near the terminal receiver to bend theconductor through an angle approaching 90. in such cases a clamp of thetype identified by the reference numeral 42 in FIG. 2 may be founduseful. This is entirely optional, however, and in most instances willbe neither necessary nor desirable.

Where laser light is transmitted by the invention arrangement, it ispossible to increase the intensity thereof at spaced-apart points alongthe power line by means of compact amplifying units of a type such asdisclosed on page 134 of the book The Laser" by W. V. Smith and P. P.Sorokin (McGraw Hill, 1966). However, this is merely exemplary of themany different expedients that can be resorted to in order to minimizeloss of data by light diminution.

Where a number of high-power transmission lines are arranged in closelyspaced parallel relationship and bear a given phase relationship to oneanother, power may be derived at'any point therealong by means of ajumper interconnecting any two of the lines. This obv viates thenecessity of developing an IR drop between the two points A and B inFIG. 2 of the drawings.

lcl l. fir: system for according to a high-power transmission line theadded capability of conveying confidential data between any two pointstherealong with assurance that the data so conveyed has not been or willnot be compromised, the combination of:

a high-power transmission line in the form of a hollow tubularconductor;

a source of optical energy modulated with confidential data to beconveyed from a first point along said high-power transmission line to asecond point along such line;

means for injecting modulated optical energy from said source into saidpower transmission line at said first point, said optical energy beingconveyed through said hollow tubular conductor to said second point;

means at said second point for receiving and detecting the opticalenergy arriving at such point;

the high power of said transmission line acting to preclude unauthorizedaccess to the said optical energy as it is conveyed within said hollowtubular conductor between said two points. i

2. A system according to claim 1 in which said hollow tubular conductoris filled with air 3. A system according to claimfin which said hollowtubular conductor is filled with a gas other than air.

4. A system according to claim 1 in which said hollow tubular conductorencloses a fiber optics bundle.

5. A system according to claim 1 in which the inner surface of saidhollow tubular conductor is highly reflective to optical energy.

6. A system according to claim 4 in which at least one light-amplifyingunit is enclosed within said hollow tubular conductor between said twopoints.

7. A system according to claim 6 in which each lightamplifying unitincludes means for detecting and demodulating the light arriving at suchunit through said fiber optics bundle, means for amplifying the light sodetected and demodulated, a source of high-intensity light, means forapplying the output of said amplifying means to modulate thehigh-intensity light output of said source, and means for returning themodulated high-intensity light to said fiber optics bundle to continueits passage to said second point.

8. The combination of claim 7 in which the energy required to operateeach said light amplifying unit is derived from the said high-powertransmission line within which such unit is enclosed.

9. The combination of claim 8 in which the energy required to operateeach said light-amplifying unit is derived from an IR drop developedbetween two spaced-apart connections to said high-power transmissionline.

10. A system according to claim 6 in which said source of optical energyis a laser, and in which each light-amplifying unit comprises a laseramplifier.

1. In a system for according to a high-power transmission line the addedcapability of conveying confidential data between any two pointstherealong with assurance that the data so conveyed has not been or willnot be compromised, the combination of: a high-power transmission linein the form of a hollow tubular conductor; a source of optical energymodulated with confidential data to be conveyed from a first point alongsaid high-power transmission line to a second point along such line;means for injecting modulated optical energy from said source into saidpower transmission line at said first point, said optical energy beingconveyed through said hollow tubular conductor to said second point;means at said second point for receiving and detecting the opticalenergy arriving at such point; the high power of said transmission lineacting to preclude unauthorized access to the said optical energy as itis conveyed within said hollow tubular conductor between said twopoints.
 2. A system according to claim 1 in which said hollow tubularconductor is filled with air.
 3. A system according to claim 1 in whichsaid hollow tubular conductor is filled with a gas other than air.
 4. Asystem according to claim 1 in which said hollow tubular conductorencloses a fiber optics bundle.
 5. A system according to claim 1 inwhich the inner surface of said hollow tubular conductor is highlyreflective to optical energy.
 6. A system according to claim 4 in whichat least one light-amplifying unit is enclosed within saiD hollowtubular conductor between said two points.
 7. A system according toclaim 6 in which each light-amplifying unit includes means for detectingand demodulating the light arriving at such unit through said fiberoptics bundle, means for amplifying the light so detected anddemodulated, a source of high-intensity light, means for applying theoutput of said amplifying means to modulate the high-intensity lightoutput of said source, and means for returning the modulatedhigh-intensity light to said fiber optics bundle to continue its passageto said second point.
 8. The combination of claim 7 in which the energyrequired to operate each said light amplifying unit is derived from thesaid high-power transmission line within which such unit is enclosed. 9.The combination of claim 8 in which the energy required to operate eachsaid light-amplifying unit is derived from an IR drop developed betweentwo spaced-apart connections to said high-power transmission line.
 10. Asystem according to claim 6 in which said source of optical energy is alaser, and in which each light-amplifying unit comprises a laseramplifier.